This invention relates to a mobile power washer for supplying pressurized hot water.
It is known to provide a high pressure power washer mounted on a trailer. A typical trailer mounted power washer may be powered by a petrol or diesel engine and be capable of delivering water supplied from a water tank through a hand held gun at a pressure of between 120 and 250 bar, and at a flow rate of between 12 and 18 liters per minute. Generally, the water supplied is untreated and therefore at ambient temperature, for example between 2° C. and 10° C.
However, hot water is sometimes required. For example, hot water is used on building sites for defrosting metal reinforcements prior to concreting and for cleaning tasks. Hot water is also required by the military, for example, for showering of soldiers in remote locations and for decontamination. There is therefore a need to provide a high pressure power washer capable of delivering hot water.
One known method of providing hot water on location is to fill the water tank of an existing trailer mounted power washer with hot water. However, this is generally inconvenient, because there may be no adequate source of hot water available, and the hot water, once in the tank of the power washer, may cool before use, particularly if the hot water source is some distance from the location where the hot water is required. Furthermore, the seals in existing washers are typically designed for use with cold water, and so may not be able to cope with hot water, for example, in excess of 50° C., and leaks may occur.
Alternatively, it is known to provide a machine providing high pressure hot water by passing a high pressure cold flow directly through a heated coil. However, machines of this type are typically large and heavy and are not particularly suitable for trailer mounting. They also require regular servicing and have a relatively short life expectancy.
WO2008/068490 discloses a trailer mounted power washer including an oil fired heater which heats a working fluid. Washing water passes through a heat exchanger where it is heated by the working fluid as the water passes from a tank to a pump and a delivery device such as a spray gun. When delivery of water is stopped, water flows through a bypass loop which incorporates a cooler to avoid friction induced overheating of the recirculating flow. A disadvantage of the power washer of WO2008/068490 is that there is a significant loss of heat from the bypass loop which cannot be recovered when delivery of water starts again.